DESCRIPTION: The specific objective of this research program is to determine whether prolonged exposure to 60 Hz linear, sinusoidal, continuous-wave magnetic fields (MFs) exerts tumor promoting effects on neurogenic tumors initiated in Fischer rats by the transplacental exposure to a subthreshold dose of a chemical carcinogen N-Ethyl-N-nitrosourea (ENU.) Their long term objective is to define both the robustness of MFs promoting effect on neurogenic tumors and determine the biological significance of such an effect. To their team, the potential carcinogenic effects of MFs has become an important issue. They have developed a major research program to evaluate the possible links between in vivo EMF exposure and related human health risks, and build a dedicated animal facility where animals could be exposed to 60 Hz MFs at different intensities under stringently controlled environment and under double-blind conditions. The present study is an integral part of this research program. It has been designed to provide direct answers to several important questions concerning the possible promoting effect of 60 Hz MFs on neurogenic tumors: 1) Can prolonged exposure to MFs promote the development of neurogenic tumors initiated by ENU in Fischer rats?; 2) In the case of tumor promotion, is there a dose response effect: MFs of 2, 20, 200, 2,000 uT will be compared to sham exposure (less than 0.02 uT)?; 3) How robust is this effect? They will estimate the bio-equivalence of MF brain tumor promotion to that of a classical promoter, TPA using a graded promotion curve. This is an important issue that could have direct implications for risk assessment; and 4) What is the biological significance of such an effect? They will determine whether MFs can induce stable and reproducible changes that favor the expression of carcinogenesis in promoted tumors by investigating the effect on ornithine decarboxylase activity, and on the expression of dominant oncogene (neu and c-myc) and tumor suppressor gene (p53.) This research program will take place in the next three years and will be co-funded by a Consortium of Canadian Sponsors and by IAF.